The quality of drinking water can be assessed by measuring an absorption spectrum of a water sample that may be contaminated by organic contaminants such as toluene. It is known in the art that ultraviolet-visible (UV-vis) and near infrared (NIR) spectroscopic methods are useful to detect such organic contaminants.
With a growing demand on assessing water quality, it is often desirable to have compact measurement devices to simultaneously, continuously and conveniently obtain and analyze water samples from many different locations. Besides, each measurement device is preferred to fit in a limited space such as a water pipe, to be light-weight and power-efficient, and to have a wide spectral and dynamic range.
In U.S. Pat. No. 6,956,648 and WO2001/46676, a miniaturized device for probing a liquid is disclosed. Two light beams are generated from a light source. One light beam passes through the liquid to give a measurement beam, and another one serves as a reference beam. A beam selector is used to select one of the two beams for sending to a spectrometer. As the spectrometer is still large, it is not convenient in operation, even if the spectrometer is remotely linked to the device through a light guide. Although reduced-size spectrometers have been developed in, e.g., U.S. Pat. No. 9,291,504, such spectrometers may still be considered too large if an integrated unit combining one such spectrometer and a light source is operated by immersing the unit into the liquid flowing along a pipe.
There is a need for a compact device for sensing a liquid in general and water in particular so that an absorption spectrum of the liquid is obtained.